U.S. patent application number 12/811045 was filed with the patent office on 2010-11-11 for semi-persistent scheduling method and apparatus based on statistically multiplexing in time and frequency resources.
Invention is credited to Tao Yang, Mingli You, Yan Zhao.
Application Number | 20100284364 12/811045 |
Document ID | / |
Family ID | 40852752 |
Filed Date | 2010-11-11 |
United States Patent
Application |
20100284364 |
Kind Code |
A1 |
You; Mingli ; et
al. |
November 11, 2010 |
SEMI-PERSISTENT SCHEDULING METHOD AND APPARATUS BASED ON
STATISTICALLY MULTIPLEXING IN TIME AND FREQUENCY RESOURCES
Abstract
A semi-persistent scheduling method and apparatus based on
statistically multiplexing in time and frequency resources, the
method comprises steps of: allocating each initial transmission to
use fixed time and frequency resources reserved for initial
transmission by using a persistent grant, and allocating each
retransmission to use time resource reserved for retransmission by
using a persistent grant and dynamically allocating each
retransmission to use frequency resource reserved for
retransmission by using a dynamic grant or a default grant, wherein
the initial transmission and the retransmission share the frequency
resources within the same time slot.
Inventors: |
You; Mingli; (Shanghai,
CN) ; Zhao; Yan; (Shanghai, CN) ; Yang;
Tao; (Shanghai, CN) |
Correspondence
Address: |
FAY SHARPE/LUCENT
1228 Euclid Avenue, 5th Floor, The Halle Building
Cleveland
OH
44115-1843
US
|
Family ID: |
40852752 |
Appl. No.: |
12/811045 |
Filed: |
December 29, 2007 |
PCT Filed: |
December 29, 2007 |
PCT NO: |
PCT/CN07/03957 |
371 Date: |
June 28, 2010 |
Current U.S.
Class: |
370/330 |
Current CPC
Class: |
H04L 1/1887 20130101;
H04Q 11/02 20130101; H04L 1/1819 20130101; H04Q 11/04 20130101;
H04Q 2213/13392 20130101; H04L 5/0053 20130101; H04Q 2213/13291
20130101; H04Q 2213/13292 20130101; H04Q 2213/13348 20130101; H04L
1/1893 20130101; H04L 5/0037 20130101; H04L 5/0044 20130101; H04Q
2213/13367 20130101 |
Class at
Publication: |
370/330 |
International
Class: |
H04W 72/04 20090101
H04W072/04 |
Claims
1. A semi-persistent scheduling method based on statistically
multiplexing in time and frequency resources, comprising steps of:
allocating each initial transmission to use fixed time and
frequency resources reserved for initial transmission by using a
persistent grant; and allocating each retransmission to use time
resources reserved for retransmission by using a persistent grant
and dynamically allocating each retransmission to use frequency
resources reserved for retransmission by using a dynamic grant or a
default grant, wherein the initial transmissions and the
retransmissions share the frequency resources within the same time
slot.
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. The semi-persistent scheduling method according to claim 1,
further comprising a step of assigning a first priority to the
initial transmissions and a second priority to the retransmissions,
in which the first priority is higher than the second priority.
9. The semi-persistent scheduling method according to claim 1,
further comprising: a step of reallocating the sizes of the
resource units, when there is a peak retransmission burstness; or a
step of temporally pausing a retransmission by using a "stop" grant
in a current time slot while maintaining its retransmission
opportunity in the next time slot, when there is a peak
retransmission burstness.
10. (canceled)
11. The semi-persistent scheduling method according to claim 1,
further comprising a step of measuring an unused resource unit
number during a predetermined measurement period, in which the
unused resource unit number is an average number of the resource
units which have not been used during the predetermined measurement
period.
12. The semi-persistent scheduling method according to claim 11,
further comprising a step of switching one user equipment into the
persistent scheduling mode if the measured unused resource unit
number is larger than a first predetermined threshold.
13. The semi-persistent scheduling method according to claim 1,
further comprising a step of measuring an unable retransmission
number during a predetermined measurement period, in which the
unable retransmission number is an average number of the
unsatisfied retransmissions during the predetermined measurement
period.
14. The semi-persistent scheduling method according to claim 13,
further comprising a step of switching one user equipment out of
the persistent scheduling mode if the measured unable
retransmission number is larger than a second predetermined
threshold.
15. (canceled)
16. A semi-persistent scheduling apparatus based on statistically
multiplexing in time and frequency resources, comprising: an
initial transmission allocating means for allocating each initial
transmission to use fixed time and frequency resources reserved for
initial transmission according to a persistent grant; and a
retransmission allocating means for allocating each retransmission
to use time resources reserved for retransmission according to a
persistent grant and dynamically allocating each retransmission to
use frequency resources reserved for retransmission according to a
dynamic grant or a default grant, wherein the initial transmission
allocating means and the retransmission allocating means
cooperatively allocate the resources so that the initial
transmissions and the retransmissions share the frequency resources
within the same time slot.
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. (canceled)
22. (canceled)
23. The semi-persistent scheduling apparatus according to claim 16,
further comprising a priority assigning means for assigning a first
priority to the initial transmissions and a second priority to the
retransmissions, in which the first priority is higher than the
second priority.
24. The semi-persistent scheduling apparatus according to claim 16,
further comprising: a means for reallocating the sizes of the
resource units, when there is a peak retransmission burstness; or a
means for temporally pausing a retransmission by using a "stop"
grant in a current time slot while maintaining its retransmission
opportunity in the next time slot, when there is a peak
retransmission burstness.
25. (canceled)
26. The semi-persistent scheduling apparatus according to claim 16,
further comprising a first measuring means for measuring an unused
resource unit number during a predetermined measurement period, in
which the unused resource unit number is an average number of the
resource units which have not been used during the predetermined
measurement period.
27. The semi-persistent scheduling apparatus according to claim 26,
further comprising a first switching means for switching one user
equipment into the persistent scheduling mode if the measured
unused resource unit number is larger than a first predetermined
threshold.
28. The semi-persistent scheduling apparatus according to claim 16,
further comprising a second measuring means for measuring an unable
retransmission number during a predetermined measurement period, in
which the unable retransmission number is an average number of the
unsatisfied retransmissions during the predetermined measurement
period.
29. The semi-persistent scheduling apparatus according to claim 28,
further comprising a second switching means for switching one user
equipment out of the persistent scheduling mode if the measured
unable retransmission number is larger than a second predetermined
threshold.
30. The semi-persistent scheduling apparatus according to claim 16,
wherein the semi-persistent scheduling apparatus is used in an
uplink voice over IP system.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to the wireless communication
field, and more particularly, to a semi-persistent scheduling
method and apparatus based on statistically multiplexing in time
and frequency resources which is used to share Hybrid Automatic
Repeat reQuest (HARQ) process resource in uplink Voice over IP
(VoIP) semi-persistent scheduling.
[0003] 2. Description of Prior Art
[0004] All services will be carried in packet domain in Long Term
Evolution (LTE) system and Voice over IP (VoIP) is an important
service for operators. The scheduling is critical to improve the
VoIP capacity with respect to the Quality of Service (QoS) and
channel information. From current 3.sup.rd Generation Partnership
Project (3GPP) status on UpLink (UL) Scheduling Principles: [0005]
1. evolved Node B (eNB) can allocate predefined uplink resources
for the first Hybrid Automatic Repeat reQuest (HARQ) transmissions
and the retransmissions to User Equipments (UEs). [0006] 2. Dynamic
scheduling can override the pre-defined allocation (persistent
allocation) for that Transmission Time Interval (TTI). eNB can
dynamically allocate resources (Physical Resource Blocks (PRBs) and
Modulation Coding Scheme (MCS)) to UEs at each TTI via the
Cell-Radio Network Temporary Identifier (C-RNTI) on L1/L2 control
channel.
[0007] With the standards defined in 3GPP, there could be 3
potential scheduling modes for uplink VoIP scheduling: [0008] 1.
Persistent scheduling which only L3 signaling allows; [0009] 2.
Dynamic scheduling which only allows to use the L1/L2 grant same
with the grant used for burst packet services such as Best effort;
[0010] 3. Semi-persistent scheduling which allows to use persistent
grant for initial transmission and dynamic grant for
retransmissions.
[0011] It is expected to support up to 400 users at the same time.
Thereafter, specifically for uplink, in order to support such large
number of VoIP users, it will consume large number of grants which
will directly reduce the downlink (DL) capacity.
[0012] The major challenge for VoIP scheduling is to increase the
system capacity with limited cost of dynamic downlink (DL) grant
signaling. With the constraints on dynamic grant method above, to
save the downlink (DL) L1 capacity, dynamic scheduling mode isn't
preferred for VoIP services. As a sequence, it becomes an issue to
leverage the unused HARQ transmission for each HARQ process.
[0013] In LTE system, low average transmission number will have
high spectrum efficiency with adaptive modulation and coding
schemes. Thus the average HARQ transmission number will be
typically between 1 and 2 to achieve good spectrum efficiency. In
other side, the maximum transmission number will be large (such as
4 or 5) for VoIP service. How to sufficiently leverage the resource
in HARQ transmission is still an open point.
[0014] To improve the resource utilization, there is a proposal
from Motorola [Reference 1] to use dynamic grouping scheduling to
group a number of VoIP users to share the resources. Different
users should use same MCS and same resource units in one group and
thus a number of groups can be defined with different MCS and RU
(resource unit) number. However, this proposal needs specific
bit-map dynamic grant to indicate which VoIP user in the group will
use the time/frequency resource.
[0015] This conflicts with current grant method in 3GPP and this
proposal isn't selected in 3GPP now.
[0016] There is another proposal from Alcatel-Lucent [Reference 2]
to share the HARQ resource with non-VoIP user. The basic idea is to
let the dynamic users use the unused HARQ retransmission
opportunities for VoIP (due to successfully transmission of the
VoIP packet) to transmit other packet service and when there is a
collision, the VoIP packet initial transmission is shifted in time
domain. But in frequency-domain, the VoIP packet will use the same
resource unit and same MCS. With this approach, the time resource
for initial transmission isn't persistent and VoIP service and
other dynamic packet services share the same frequency resource.
This seems also not feasible from current 3GPP status and system
design viewpoint in the case that there is different Bandwidth
allocated to VoIP services and other burst services.
[0017] Although principally, it is possible to apply dynamic
scheduling for VoIP services as other dynamic packet services such
as best effort, with consideration on strict latency and
requirement to support large number of VoIP users simultaneously,
this pure dynamic scheduling mode is totally not efficient from
signaling cost viewpoint and thus not a preferred solution at least
for LTE R8.
[0018] How to improve the resource utilization of VoIP packet HARQ
transmission is still an open point.
[0019] In this invention, an enhanced semi-persistent scheduling
method based on statistically multiplexing in time and frequency
resources are proposed with its target to achieve good trade-off
between the system VoIP capacity and reasonable grants cost.
SUMMARY OF THE INVENTION
[0020] This basic idea of the present invention is to statistically
leverage the unused HARQ transmission opportunities through TDM and
FDM among VoIP UEs in the semi-persistent scheduling mode for
uplink VoIP scheduling.
[0021] In details, according to a first aspect, the present
invention proposes a semi-persistent scheduling method based on
statistically multiplexing in time and frequency resources,
comprising steps of: allocating each initial transmission to use
fixed time and frequency resources reserved for initial
transmission by using a persistent grant; and allocating each
retransmission to use time resources reserved for retransmission by
using a persistent grant and dynamically allocating each
retransmission to use frequency resources reserved for
retransmission by using a dynamic grant or a default grant, wherein
the initial transmissions and the retransmissions share the
frequency resources within the same time slot.
[0022] Preferably, the initial transmissions are uniformly
distributed into different time slots.
[0023] Preferably, the fixed frequency resources allocated for the
initial transmissions in each time slot are in a random manner or a
cyclic-shift manner.
[0024] Preferably, the time resources are different time slots, and
the frequency resources include different modulation coding schemes
and different resource units. More preferably, the time resources
are allocated in a persistent scheduling mode by using the
persistent grant, whereas the frequency resources reserved for the
initial transmissions are allocated in a persistent scheduling mode
by using the persistent grant, and the frequency resources reserved
for the retransmissions are allocated in a dynamic scheduling mode
by using the dynamic grant or the default grant. More preferably,
the modulation coding scheme and the number of the resource units
allocated to the retransmission are dynamically changed by the
dynamic grant. More preferably, the modulation coding scheme and
the number of the resource units allocated to the initial
transmission are slowly changed by the persistent grant.
[0025] Preferably, the semi-persistent scheduling method further
comprises a step of assigning a first priority to the initial
transmissions and a second priority to the retransmissions, in
which the first priority is higher than the second priority.
[0026] Preferably, the semi-persistent scheduling method further
comprises: a step of reallocating the sizes of the resource units,
when there is a peak retransmission burstness; or a step of
temporally pausing a retransmission by using a "stop" grant in a
current time slot while maintaining its retransmission opportunity
in the next time slot, when there is a peak retransmission
burstness. More preferably, the "stop" grant is a general dynamic
grant with a "zero" resource unit number and a "zero"-numbered
modulation coding scheme.
[0027] Preferably, the semi-persistent scheduling method further
comprises a step of measuring an unused resource unit number during
a predetermined measurement period, in which the unused resource
unit number is an average number of the resource units which have
not been used during the predetermined measurement period. More
preferably, the semi-persistent scheduling method further comprises
a step of switching one user equipment into the persistent
scheduling mode if the measured unused resource unit number is
larger than a first predetermined threshold.
[0028] Preferably, the semi-persistent scheduling method further
comprises a step of measuring an unable retransmission number
during a predetermined measurement period, in which the unable
retransmission number is an average number of the unsatisfied
retransmissions during the predetermined measurement period. More
preferably, the semi-persistent scheduling method further comprises
a step of switching one user equipment out of the persistent
scheduling mode if the measured unable retransmission number is
larger than a second predetermined threshold.
[0029] Preferably, the semi-persistent scheduling method is used
for an uplink voice over IP service.
[0030] On the other hand, according to a second aspect, the present
invention also proposes a semi-persistent scheduling apparatus
based on statistically multiplexing in time and frequency
resources, comprising: an initial transmission allocating means for
allocating each initial transmission to use fixed time and
frequency resources reserved for initial transmission according to
a persistent grant; and a retransmission allocating means for
allocating each retransmission to use time resources reserved for
retransmission according to a persistent grant and dynamically
allocating each retransmission to use frequency resources reserved
for retransmission according to a dynamic grant or a default grant,
wherein the initial transmission allocating means and the
retransmission allocating means cooperatively allocate the
resources so that the initial transmissions and the retransmissions
share the frequency resources within the same time slot.
[0031] Preferably, the initial transmission allocating means
uniformly distributes the initial transmissions into different time
slots.
[0032] Preferably, the initial transmission allocating means
allocates the fixed frequency resources for the initial
transmissions in each time slot in a random manner or a
cyclic-shift manner.
[0033] Preferably, the time resources are different time slots, and
the frequency resources include different modulation coding schemes
and different resource units. More preferably, the initial
transmission allocating means allocates the time and frequency
resources in a persistent scheduling mode according to the
persistent grant, whereas the retransmission allocating means
allocates the time resources in a persistent scheduling mode
according to the persistent grant and allocates the frequency
resources in a dynamic scheduling mode according to the dynamic
grant or the default grant. More preferably, the retransmission
allocating means dynamically changes the modulation coding scheme
and the number of the resource units to be allocated to the
retransmission according to the dynamic grant. More preferably, the
initial transmission allocating means slowly changes the modulation
coding scheme and the number of the resource units to be allocated
to the initial transmission according to the persistent grant.
[0034] Preferably, the semi-persistent scheduling apparatus further
comprises a priority assigning means for assigning a first priority
to the initial transmissions and a second priority to the
retransmissions, in which the first priority is higher than the
second priority.
[0035] Preferably, the semi-persistent scheduling apparatus further
comprises: a means for reallocating the sizes of the resource
units, when there is a peak retransmission burstness; or a means
for temporally pausing a retransmission by using a "stop" grant in
a current time slot while maintaining its retransmission
opportunity in the next time slot, when there is a peak
retransmission burstness. More preferably, the "stop" grant is a
general dynamic grant with a "zero" resource unit number and a
"zero"-numbered modulation coding scheme.
[0036] Preferably, the semi-persistent scheduling apparatus further
comprises a first measuring means for measuring an unused resource
unit number during a predetermined measurement period, in which the
unused resource unit number is an average number of the resource
units which have not been used during the predetermined measurement
period. More preferably, the semi-persistent scheduling apparatus
further comprises a first switching means for switching one user
equipment into the persistent scheduling mode if the measured
unused resource unit number is larger than a first predetermined
threshold.
[0037] Preferably, the semi-persistent scheduling apparatus further
comprises a second measuring means for measuring an unable
retransmission number during a predetermined measurement period, in
which the unable retransmission number is an average number of the
unsatisfied retransmissions during the predetermined measurement
period. More preferably, the semi-persistent scheduling apparatus
further comprises a second switching means for switching one user
equipment out of the persistent scheduling mode if the measured
unable retransmission number is larger than a second predetermined
threshold.
[0038] Preferably, the semi-persistent scheduling apparatus is used
in an uplink voice over IP system.
[0039] In the semi-persistent scheduling mode, multiple VoIP users
share the same HARQ process within one Voice Frame (20 ms) through
time division multiplexing (TDM). Different VoIP UEs' initial
transmission can be allocated into different time slots of the same
HARQ process by using the persistent grant. In frequency-domain,
the resource units (RUs) are used as pool to be shared by VoIP UEs.
A part of the frequency resource (Resource Unit) is reserved for
initial VoIP packet transmission and the left part will be used for
VoIP packet retransmission. The RUs reserved for initial
transmissions are allocated by persistent grant and the RUs for
retransmissions are statistically shared among different VoIP UEs
using dynamic grant. The frequency-domain shifting can be used to
avoid the confliction between retransmission and initial
transmission.
[0040] To well balance the ratio of RUs for initial transmission
and RUs for retransmissions, there introduces a outer control loop
to well adjust the balance between the number of supportable VoIP
users within one HARQ process and the outage probability of VoIP
service by monitoring the "unused resource unit" and "unable HARQ
retransmission" probability. To avoid the confliction of the burst
retransmission peak, a "stop grant" can be introduced in current
3GPP-defined grant to postpone HARQ retransmission temporarily.
[0041] With the above approach according to the present invention
to improve resource utilization for HARQ process for
semi-persistent uplink VoIP scheduling, the present invention has
the following benefits: [0042] Significantly reduce the dynamic
signaling grant cost by persistently allocating multiple VoIP UEs
to share the same HARQ process for their initial transmissions; In
addition, the waste of unused HARQ process is minimized due to the
multiplexing in time domain for initial transmissions among
multiple VoIP UEs. [0043] Further improve the VoIP capacity due to
the multiplexing gain of HARQ retransmission by statistically
multiplexing multiple VoIP packet retransmission in a limited
frequency-domain resource pool. Since the VoIP packets
retransmission is a random event, it doesn't need to reserve same
number of RUs for retransmission as their initial transmissions;
[0044] Introduce a "stop" grant to avoid the confliction of initial
transmission and retransmission burst peak; [0045] The outer
control loop to adjust the balance of RUs for initial transmission
and retransmission can make the VoIP capacity close to the pure
dynamic scheduling mode but with moderate grant cost only.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] The above and other objects, features and advantages of the
present invention will be clearer from the following detailed
description about the non-limited embodiments of the present
invention taken in conjunction with the accompanied drawings, in
which:
[0047] FIG. 1 is a schematic diagram to overview the
characteristics of the VoIP service from VoIP data source;
[0048] FIG. 2 is a flowchart to illustrate the operation following
the semi-persistent scheduling method according to the present
invention;
[0049] FIG. 3 is a schematic diagram to illustrate an example for
statistically HARQ process sharing using TDM/FDM;
[0050] FIG. 4 is a block diagram to illustrate the structure of the
semi-persistent scheduling apparatus according to the present
invention; and
[0051] FIG. 5 shows the system simulation results of the inventive
semi-persistent scheduling method and the comparative persistent
scheduling method.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0052] Hereunder, the present invention will be described in
accordance with the drawings. In the following description, some
particular embodiments are used for the purpose of description
only, which shall not be understood as any limitation to the
present invention but the examples thereof. While it may blur the
understanding of the present invention, the conventional structure
or construction will be omitted.
1. VoIP Service Characteristics
[0053] For VoIP service, there are two states either talk state or
silence state. In talk state, only one VoIP packet is transmitted
every 20 ms; and in silence state, one SID (silence descriptor)
packet is transmitted every 160 ms as shown in FIG. 1. In addition,
the synchronous HARQ is supported for UL VoIP transmission.
2. Sharing HARQ Transmission Using TDM/FDM Method for
Semi-Persistent Scheduling Mode
[0054] The semi-persistent scheduling is a preferred solution for
LTE uplink VoIP scheduling due to its property of good trade-off
between capacity and dynamic signaling cost. The traditional
approach for semi-persistent scheduling is to reserve the first
time slot within HARQ process for initial transmission and the left
time slots will be reserved for HARQ retransmission. If the VoIP
packet transmission is successful, the left HARQ retransmission
opportunities will be used for another VoIP user using dynamic
L1/L2 grant. Then in next time slot, the new VoIP user's
retransmission may conflict with the reserved initial transmission.
In addition, for the same VoIP user, it is hard to determine
whether its initial transmission will be dynamically scheduled
through dynamic grant or will be persistent scheduled with L3
signaling.
[0055] The basic idea in this proposed approach is to share the
HARQ process among multiple VoIP users in TDM to improve VoIP UE
capacity while avoiding VoIP user's initial transmission to be
dynamically scheduled: [0056] Each initial transmission uses fixed
time, fixed resource (RU+MCS) from persistent grant; [0057]
Multiple VoIP users can start initial transmission in different
time slots in the HARQ process; [0058] The distribution of initial
transmission should be uniform in different time slots. [0059]
Initial transmission and retransmission share the frequency
resource within the same time slot: a part of resource is reserved
for initial transmission and the left part will be reserved for
retransmission only. [0060] The allocation of frequency resource in
persistent scheduling for initial transmission in each time slot
could be in a random or cyclic-shift manner depending on the
trade-off between signaling cost for retransmission and
frequency-diversity gain. [0061] The time resource is persistent
while the frequency-domain resource reallocation could be dynamic;
[0062] Both MCS and RU number can be dynamically changed through
dynamic grant for HARQ retransmission: Frequency-selective
scheduling can be applied for HARQ retransmission; [0063] Only
slowly change is allowed for initial transmission by using
persistent grant. [0064] If there is confliction between VoIP
initial transmission and VoIP retransmission, the initial
transmission has a higher priority than retransmission: [0065] The
initial transmission can be guaranteed with persistent scheduling;
[0066] If there is a peak retransmission burstness, either
reallocating the RU size or temporally pausing the retransmission
with "stop" grant while maintaining its retransmission opportunity
in the next time slot. The "stop" grant is a general dynamic grant
with "zero" RU number and MCS.
[0067] FIG. 2 is a flowchart to illustrate the operation following
the semi-persistent scheduling method according to the present
invention.
[0068] In details, at step 201, each initial transmission is
allocated to use fixed time and frequency resources reserved for
initial transmission by using a persistent grant. Then, at step
203, each retransmission is allocated to use time resources
reserved for retransmission by using a persistent grant and is
dynamically allocated to use frequency resources reserved for
retransmission by using a dynamic grant or a default grant. Herein,
the initial transmissions and the retransmissions share the
frequency resources within the same time slot.
[0069] At step 205, it is judged whether the initial transmissions
are conflicting with those retransmissions in a current time slot.
If it is determined that these transmissions (initial transmissions
and the retransmissions) are conflicting with each other ("Yes" at
step 205), then at step 207, it will determine that the initial
transmissions have a higher priority and will be firstly
transmitted, and the retransmissions will be waiting for a next
transmission opportunity coming in the next time slot. Otherwise,
if it is determined that the transmissions are not conflicting with
each other ("No" at step 205), then at step 209, the unused RU
number and the unable HARQ retransmission number are measured
during a predetermined measurement period.
[0070] Thereafter, at step 211, it is judged whether the unused RU
number is larger than a predetermined threshold A (will be
described later). If so ("Yes" at step 211), at step 213, one UE is
added into the persistent scheduling mode, i.e., switching one UE
into the persistent scheduling mode, and then the process goes back
to the step 201 to perform the process with the updated UE number.
Otherwise ("No" at step 211), the process directly goes back to the
step 201 to perform the initial transmission allocation with the
non-updated UE number.
[0071] On the other hand, at step 215, it is judged whether the
unable HARQ retransmission number is larger than a predetermined
threshold B (will be described later). If so ("Yes" at step 215),
at step 217, one UE in the persistent scheduling mode is removed,
i.e., switching one UE out of the persistent scheduling mode, and
then the process goes back to the step 201 to perform the process
with the updated UE number. Otherwise ("No" at step 215), the
process directly goes back to the step 201 to perform the initial
transmission allocation with the non-updated UE number.
[0072] FIG. 3 illustrates an example that 8 VoIP users share the 4
RUs (resource units) with the same HARQ process 1. Several RUs
(those circled with dashed ellipses) are reserved for persistent
scheduling for initial transmission and the left RUs (those shaded)
are used for HARQ retransmission and thus can be dynamically
scheduled.
[0073] In the example shown in FIG. 3, we have 8 VoIP UEs which
share the 4 Resource units (RU) in the HARQ process 1. In this
example, 8 VoIP UEs' initial transmission is using persistent grant
and uniformly distributed in the 4 timeslots such as, [0074] In the
first time slot of HARQ process 1, the first two resource units are
reserved for UE1 and UE4 using persistent grant while the left 2
RUs are used for retransmission either by dynamic grant or default
grant. [0075] In the second time slot of HARQ process 1, the first
two RUs are used for retransmission and the left 2 RUs are reserved
for initial transmission of UE2 and UE5. Since the UE1 and UE4's
retransmission are on the same RU and thus no need for dynamic
grant which can reduce the grant overhead. [0076] In the third time
slot of HARQ process 1, similarly, two RUs are reserved for UE3 and
UE6's initial transmission by persistent grant, while UE2 and UE5
have their retransmission in the remaining RUs. Here both UE2 and
UE5 use different RU by dynamic grant where they can get some
frequency-diversity gain through frequency-hopping manner with some
grant overhead cost. [0077] In the fourth timeslot of HARQ process
1, similarly, UE7 and UE8's initial transmission are reserved and
UE3's retransmission is scheduled with default grant. The left RU
is used for UE5's second retransmission and UE6 has its first
transmission successfully.
[0078] With this method, the retransmissions among different VoIP
UEs can be statistically multiplexed in the same HARQ process with
frequency-shifting. Also with frequency-shifting, certain degree of
frequency diversity gain can be achieved through frequency-hopping.
The ratio between the number of RUs reserved for initial
transmission and the number of RUs reserved for retransmission is
determined by VoIP capacity and the configured RUs for VoIP service
and can be slowly adjusted in semi-static manner as defined
above.
[0079] There needs an outer control loop to manage the total number
of VoIP UEs for the HARQ process in order to guarantee the target
VoIP service QoS: [0080] The number of VoIP UEs can be increased or
decreased for the HARQ process depending on the measurement of
"unused RU number" and "unable HARQ retransmission"; [0081] The
"unused RU number" is the average resource units which have not
been used in the HARQ process during the measurement period. If
"unused RU number">threshold A, add one VoIP UE in the
persistent scheduling for the HARQ process, here threshold A is a
pre-defined parameter [0082] The "unable HARQ retransmission" is
the average number of unsatisfied HARQ retransmission request due
to limited resource in the HARQ process during the measurement
period. If "unable HARQ retransmission">threshold B, remove one
VoIP UE in the persistent scheduling for the HARQ process, here,
threshold B is another pre-defined parameter.
[0083] Both threshold A and threshold B are derived from system
simulations according to the trade-off between RU utilization
efficiency and VoIP QoS guarantees.
[0084] FIG. 4 is a block diagram to illustrate the structure of the
semi-persistent scheduling apparatus according to the present
invention.
[0085] The semi-persistent scheduling apparatus 400 according to
the present invention includes an initial transmission allocating
unit 410, a retransmission allocating unit 420, a priority
assigning unit 430, a measuring unit 440 and a switching unit
450.
[0086] The initial transmission allocating unit 410 allocates each
initial transmission to use fixed time and frequency resources
reserved for initial transmission according to a persistent grant.
The retransmission allocating unit 420 allocates each
retransmission to use time resources reserved for retransmission
according to a persistent grant and dynamically allocates each
retransmission to use frequency resources reserved for
retransmission according to a dynamic grant or a default grant.
Herein, the initial transmissions and the retransmissions share
frequency resources within the same time slot.
[0087] The priority assigning unit 430 assigns a higher priority to
the initial transmissions than the retransmissions. So, when the
initial transmissions are conflicting with those retransmissions in
a current time slot, it will determine that the initial
transmissions have the higher priority and will be firstly
transmitted, and the retransmissions will be waiting for a next
transmission opportunity coming in the next time slot.
[0088] The measuring unit 440 measures the unused RU number and the
unable HARQ retransmission number during a predetermined
measurement period.
[0089] The switching unit 450 switches the UE into/out of the
persistent scheduling mode according to the measurement results of
the measuring unit 440. When the unused RU number is larger than a
predetermined threshold A (will be described later), the switching
unit 450 adds one UE into the persistent scheduling mode, i.e.,
switches one UE into the persistent scheduling mode, and then
notifies the initial transmission allocating unit 410 and the
retransmission allocating unit 420 to perform their resource
allocations with the updated UE number. On the other hand, when the
unable HARQ retransmission number is larger than a predetermined
threshold B (will be described later), the switching unit 450
removes one UE in the persistent scheduling mode, i.e., switches
one UE out of the persistent scheduling to mode, and then notifies
the initial transmission allocating unit 410 and the retransmission
allocating unit 420 to perform their resource allocations with the
updated UE number. Otherwise, if the unused RU number is not larger
than the predetermined threshold A and the unable HARQ
retransmission number is not larger than the predetermined
threshold B, the switching unit 450 will perform no switching
operations and notify the initial transmission allocating unit 410
and the retransmission allocating unit 420 to perform their
resource allocations with the non-updated UE number.
3. Preliminary Simulation Results
[0090] FIG. 5 shows the system simulation results of the inventive
semi-persistent scheduling method and the comparative persistent
scheduling method, with the following system simulation parameters:
[0091] 19 cells with 3 sectors (1 cell with VoIP UEs, others with 5
Full Buffer UEs using Round-robin scheduler) [0092] 40 bytes voice
packet, 15 bytes SID packet [0093] 6 HARQ processes, fixed QPSK
2/3*2 RUs for VoIP packet, [0094] Fractional PC (Target loT 4.5 dB)
[0095] Static IC using 1/3 FFR for cell-edge UEs [0096] Voice
activity (50%) [0097] 22 RUs data transmission
[0098] In FIG. 5, UL VoIP Capacity for 12.2 Kbps AMR in Case 1
(with SID, 5 MHz Bandwidth) is about 240 UEs with satisfied VoIP
QoS for the proposed semi-persistent scheduling (the middle
triangle indicia). The capacity is about double as the persistent
scheduling due to the efficient usage of unused HARQ resource in
statistical method.
[0099] The above embodiments are provided for the purpose of
example only, and are not intended to limit the present invention.
It is to be understood by those skilled in the art that there may
be various modifications or replacements to the embodiments without
departing from the scope and the spirit of the present invention,
and they shall fall into the scope defined by the appended
claims.
REFERENCE LIST
[0100] Reference 1: R2-070908 Group scheduling E-UTRA VoIP,
Motorola; [0101] Reference 2: R2-072667 Efficient Persistent UL
Scheduling and HARQ Feedback Usage, Alcatel-Lucent
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